OBJECTIVE: To evaluate the relationship between the parenting style of an adolescent's peers' parents and an adolescent's substance use.DESIGN: Longitudinal survey.SETTING: Adolescents across the United States were interviewed at school and at home.PARTICIPANTS: Nationally representative sample of adolescents in the United States.MAIN EXPOSURE: Authoritative vs neglectful parenting style of adolescent's parents and adolescent's friends' parents and adolescent substance use.MAIN OUTCOME MEASURES: Adolescent alcohol abuse, smoking, marijuana use, and binge drinking.RESULTS: If an adolescent had a friend whose mother was authoritative, that adolescent was 40% (95% CI, 12%-58%) less likely to drink to the point of drunkenness, 38% (95% CI, 5%-59%) less likely to binge drink, 39% (95% CI, 12%-58%) less likely to smoke cigarettes, and 43% (95% CI, 1%-67%) less likely to use marijuana than an adolescent whose friend's mother was neglectful, controlling for the parenting style of the adolescent's own mother, school-level fixed effects, and demographics. These results were only partially mediated by peer substance use.CONCLUSIONS: Social network influences may extend beyond the homogeneous dimensions of own peer or own parent to include extradyadic influences of the wider network. The value of parenting interventions should be reassessed to take into account these spillover effects in the greater network.